Qatadah and Ata' (may Allah have mercy on them both) say regarding a man who makes a contract of manumission (mukatabah) with two slaves together on the condition that the living one of you is responsible for the dead one of you, and the destitute one of you is the responsibility of the wealthy one of you: They both said: This is not permissible.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب المكاتب / 21635